Lubricant compositions

ABSTRACT

Lubricant compositions containing (a) a mineral and/or synthetic base oil and (b) at least one compound of the formula I ##STR1## wherein a is 0 or 1, b is 1 to 6, R is H or alkoxycarbonyl, R 1  and R 2  are independently alkyl, cycloalkyl, aryl, aralkyl or are together substituted alkylene and X is hydroxyl, alkoxy, aryloxy, amino, substituted amino or the residue of a polyol, are described.

The present invention relates to lubricant compositions containing monothiophosphoric acid ester derivatives.

Mineral and synthetic lubricants generally have added various additives to improve their end-use properties. There is in particular a need for additives which reduce the coefficient of friction. Such additives must additionally increase the load-bearing capacity of the lubricant, be noncorrosive in respect of the metal components to be protected, and be highly heat-resistant.

Various lubricant additives have already been proposed, examples being the various dithiophosphoric acid derivatives described in German Pat. No. 2,104,041 and German Offenlegungsschrift No. 2,756,488. The properties of such additives in lubricating oils are frequently unsatisfactory. In particular, the friction-reducing action or the thermal resistance is not as high as it should be.

It has now been found that certain ashfree monothiophosphoric acid esters of the formula I have a clearly better friction-reducing action in the mixed friction field at elevated temperatures in mineral and synthetic lubricants than have either the zinc dithiophosphates or the corresponding metalfree dithiophosphates.

The invention accordingly provides lubricant compositions containing (a) a mineral and/or synthetic base oil and (b) at least one compound of the formula I ##STR2## in which a is 0 or 1, b is an integer from 1 to 6, R is --H, --CH₃, --COOH, C₂ -C₁₃ -alkoxycarbonyl where the alkyl radical can be interrupted by one or two oxygen atoms, or C₆ -C₁₃ -cycloalkoxycarbonyl, and R¹ and R², independently of each other, are each C₃ -C₁₂ -alkyl which can be interrupted by one or two oxygen or sulfur atoms, C₅ -C₁₂ -cycloalkyl, phenyl which is unsubstituted or substituted by one to three C₁ -C₁₂ -alkyl groups, or C₇ -C₉ -phenylalkyl, and R¹ and R² together can be a bifunctional radical of the formula II ##STR3## where n is 0 or 1, R³, R⁴, R⁵ and R⁶, independently of each other, are each --H, C₁ -C₄ -alkyl, C₅ -C₁₂ -cycloalkyl or phenyl, and R⁷ and R⁸, independently of each other, are each --H, C₁ -C₄ -alkyl, phenyl, --NO₂, C₂ -C₁₉ -alkoxycarbonyl or C₆ -C₁₃ -cycloalkoxycarbonyl, or R⁷ and R⁸, together with the carbon atom to which they are bonded, are a cyclopentenyl or cyclohexenyl ring, X, if b=1, is --OR⁹ or --N(R¹⁰)(R¹¹), where R⁹ is --H, C₁ -C₂₂ -alkyl, C₅ -C₁₂ -cycloalkyl or phenyl, and R¹⁰ and R¹¹, independently of each other, are each --H, C₁ -C₂₂ -alkyl which is unsubstituted or interrupted by one or two oxygen atoms, C₂ -C₂₂ -alkenyl or C₅ -C₁₂ -cycloalkyl, or R¹⁰ and R¹¹, together with the nitrogen atom to which they are bonded, are a C₂ -C₂₂ -alkylene or C₂ -C₂₂ -alkenylene ring which can be interrupted by oxygen, sulfur and/or nitrogen atoms, and X, if b>1, is a polyvalent radical of the formulae --OC_(m) H_(2m) O--, where the C_(m) H_(2m) group can be interrupted by one or 2 oxygen or sulfur atoms, --OCH₂ --C(R¹²)(R¹³)--CH₂ O--, ##STR4## (--OCH₂)₃ C--R¹⁴, (--OCH₂)₄ C or (--OCH₂)₃ C--CH₂ --O--CH₂ --C(CH₂ O--)₃, where m is an integer from 2 to 40, and R¹² and R¹³ are each C₁ -C₄ -alkyl, C₂ -C₉ -alkoxycarbonyl, C₆ -C₁₃ -cycloalkoxycarbonyl, phenyl or --NO₂, or R¹² and R¹³, together with the carbon atom to which they are bonded, are a cyclopentenyl ring, and R¹⁴ is --CH₃ or --C₂ H₅.

R¹ to R¹³ can be straight-chain or branched alkyl, for example, in the case of R³ to R¹³, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec.-butyl and tert.-butyl, in the case of R⁹ in the --OR⁹ radical and R¹⁰ and R¹¹, in addition n-pentyl, tert.-pentyl, n-hexyl, 1- and 6-methylpentyl, n-octyl, 2-ethylhexyl, 1,1-dimethylhexyl, n-decyl, n-dodecyl, 2-ethyldecyl, 1,1,7,7-tetramethyloctyl, n-tetradecyl, n-hexadecyl, n-octadecyl and eicosyl, but in particular, in the case of R⁹, C₁ -C₁₃ -alkyl.

C₃ -C₁₂ -alkyl radicals R¹ and R² can be the same radicals which have already been mentioned as having 3 to 12 C atoms.

In the case of R¹ and R² being alkyl substituted by one or two oxygen or sulfur atoms, they can be, for example, alkoxyalkyl and alkylthioalkyl groups, in particular alkoxyalkyl having a total of 3-12 C atoms, such as 2-methoxyethyl, 2-ethoxyethyl, 2-n-propoxyethyl, 2-isopropoxyethyl, 2-n-butoxyethyl, 2-n-octoxyethyl and methoxypropyl, as well as diethylene glycol monoalkyl ether groups such as β-methoxyethoxyethyl, β-ethoxyethoxyethyl and β-n-butyloxyethoxyethyl. A particular mention should go to compounds in which R¹ and R² are each alkoxyalkyl having 3-6 C atoms. In the case of R¹⁰ and R¹¹ being alkyl interrupted by one or two oxygen atoms, they can be the same radicals as have already been mentioned.

C₅ -C₁₂ -cycloalkyls R¹, R², R³ to R⁶, R¹⁰ and R¹¹ can be for example cyclopentyl, cyclohexyl, monomethylcyclohexyl, dimethylcyclohexyl, cyclooctyl, cyclodecyl or cyclododecyl. Cyclohexyl is preferred.

A C₅ -C₁₂ -cycloalkyl R⁹ can be one of the radicals already mentioned, but in particular C₆ -C₉ -cycloalkyl.

C₂ -C₂₂ -alkenyls R¹⁰ and R¹¹ can be straight-chain or branched substituents having one or more double bonds, preferably one or two, for example 2-butenylene, 3-butenylene, 4-butenylene, 2-pentenylene, 3-pentenylene or 4-pentenylene.

In the case of R¹ and R² being phenyl substituted by one to three alkyl groups they can be for example methyl, ethyl, isopropyl, n-butyl, sec.-butyl, tert.-butyl, tert.-pentyl, n-hexyl, n-octyl, 1,1,3,3-tetramethylbutyl or 1,1,3,3,5,5-hexamethylhexyl groups.

C₇ -C₉ -phenylalkyls R¹ and R² can be α,α-dimethylbenzyl, β-phenylethyl and in particular benzyl. C₂ -C₁₉ -alkoxycarbonyls R⁷ and R⁸ can be for example methoxycarbonyl, ethoxycarbonyl, butoxycarbonyl, hexoxycarbonyl, octoxycarbonyl, dodecyloxycarbonyl or octyldecyloxycarbonyl. Preferred alkoxycarbonyl groups contain 2 to 9 C atoms, but in particular 2 to 5 C atoms.

C₂ -C₁₃ - or C₂ -C₉ -alkoxycarbonyls R, R¹² and R¹³ can be the same radicals as have already been mentioned as having 2 to 13 C or 2 to 9 C atoms respectively. C₂ -C₅ -alkoxycarbonyl is preferred. C₆ -C₁₃ -cycloalkoxycarbonyls R, R⁷, R⁸, R¹² and R¹³ can be for example cyclopentoxy, cyclohexoxy, trimethylcyclohexoxy or cycloheptoxycarbonyl, but in particular cyclohexoxycarbonyl.

An --OC_(m) H_(2m) O-- X contains as C_(m) H_(2m) radical for example ethylene, 1,2-propylene, 3-methyl-1,3-propylene, 1,4-butylene, 1,5-pentylene, 1,6-hexamethylene, 2-methylethylene, 2-ethylethylene, 2-eicosylethylene, 1,2-dimethylethylene, 1,1,2,2-tetramethylethylene, 3-methyl-1,3-pentylene or 3-tert.-butyl-1,3-pentylene. An --OC_(m) H_(2m) O-- radical which is interrupted by oxygen or sulfur atoms can be for example [--O--CH(CH₃)--CH₂ --₂ O, [--O--CH(CH₃)--CH₂ --₂ S or --OC₂ H₄ OC₂ H₄ OC₂ H₄ O--.

R⁷ and R⁸, together with the C atom to which they are bonded, can be for example 2- or 3-cyclopenten-1-yl or 3-cyclohexen-1-yl.

R¹⁰ and R¹¹ in the form of C₂ -C₂₂ -alkylene or C₂ -C₂₂ -alkenylene are, together with the N atom to which they are bonded, a ring which can be interrupted by one or more atoms from the group comprising oxygen, sulfur and nitrogen. The alkylene or alkenylene portion of this ring can be monosubstituted or polysubstituted by C₁ -C₄ -alkyl, such as C₁ -C₄ -alkylated 1,4-butylene or 1,5-pentylene, in particular methylated 1,4-butylene or 1,5-pentylene. The alkenylene portion of the ring can have one or two double bonds and be for example 2-butenylene, 3-butenylene, 4-butenylene, 2-pentenylene, 3-pentenylene or 4-pentenylene. Such a heterocyclic ring which is also interrupted by additional O, S and/or N atoms can be, together with the N atom linking R¹⁰ and R¹¹, in particular morpholino, thiomorpholino, piperazino, 4-methylpiperazino, pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, tetrazole, 2-imidazoline, 4-imidazoline, 2H,6H-1,5,2-dithiazine, pyraline, 3-pyrazoline or 2-pyrazoline.

Preferred lubricant compositions contain at least one compound of the formula I in which a is 0, b is an integer from 1 to 4, R is --H or C₂ -C₅ -alkoxycarbonyl, and R¹ and R², independently of each other, are each C₃ -C₁₂ -alkyl which can be interrupted by one or two oxygen atoms, cyclohexyl, phenyl which is unsubstituted or substituted by one to three C₁ -C₁₂ -alkyl groups, or benzyl, or R¹ and R² together can be a bifunctional radical of the formula II ##STR5## where n is 0 or 1, R³, R⁴, R⁵ and R⁶, independently of each other, are each --H, --CH₃ or --C₂ H₅, R⁷ and R⁸, independently of each other, are each --H, C₁ -C₄ -alkyl, phenyl, --NO₂ or C₂ -C₉ -alkoxycarbonyl, or R⁷ and R⁸, together with the carbon atom to which they are bonded, are a cyclohexenyl ring, and X, if b=1, is --OR⁹ or --N(R¹⁰)R¹¹) where R⁹ is --H, C₁ -C₁₃ -alkyl or C₆ -C₉ -cycloalkyl, and R¹⁰ and R¹¹ are each --H, or R¹⁰ and R¹¹, together with the nitrogen atom to which they are bonded, are a C₄ -C₆ -alkylene ring which can be interrupted by oxygen, sulfur or nitrogen atoms, and X, if b>1, is a polyvalent radical of the formula --OC_(m) H_(2m) O-- where the C_(m) H_(2m) group can be interrupted by one or two oxygen or sulfur atoms and m is a number from 4 to 6, or X is --OCH₂ --C(R¹²)(R¹³)--CH₂ O--, (--OCH₂)₃ C--R¹⁴ or (--OCH.sub. 2)₄ C, where R¹² and R¹³ are each C₁ -C₄ -alkyl or C₂ -C₄ -alkoxycarbonyl, or R¹² and R¹³, together with the carbon atom to which they are bonded, are a cyclopentenyl ring, and R¹⁴ is --CH₃ or --C₂ H₅.

Particularly preferred lubricant compositions contain at least one compound of the formula I in which a and b are as defined above, R is --H, and R¹ and R², independently of each other, are each C₃ -C₁₂ -alkyl, cyclohexyl or phenyl which is unsubstituted or substituted by 1 to three C₁ -C₁₂ -alkyl groups, or R¹ and R² together are a bifunctional radical of the formula II where n is 1, R³, R⁴, R⁵ and R⁶ are each --H and R⁷ and R⁸ are each C₁ -C₄ -alkyl or C₂ -C₃ -alkoxycarbonyl, and X, if b=1, is --OR⁹ or --N(R¹⁰)(R¹¹) where R⁹ is --H, C₁ -C₁₃ -alkyl or C₆ -C₉ -cyclohexyl and R¹⁰ and R¹¹ are each --H, or R¹⁰ and R¹¹, together with the nitrogen atom to which they are bonded, are morpholino, thiomorpholino, piperazino or 4-methylpiperazino, and X, if b>1, is a polyvalent radical of the formulae --OC_(m) H_(2m) O--, (--O--C₂ H₄)₂ O or (--OCH₂)₄ C, where m is an integer from 4 to 6.

In likewise preferred compounds of the formula I, X, if b=1, is --OR⁹ and X, if b>1, is a polyvalent radical of the formulae --OC_(m) H_(2m) O--, --OCH₂ --C(R¹²)(R¹³)--CH₂ O--, ##STR6## (--OCH₂)₃ C--R¹⁴, (--OCH₂)₄ C or (--OCH₂)₃ C--CH₂ --O--CH₂ --C(CH₂ O--)₃, and R⁹, R¹², R¹³, R¹⁴ and m are as defined on pages 2 and 3. b is preferably 1.

In non-limiting examples of compounds of the formula I the symbols are defined as follows:

    __________________________________________________________________________     R.sup.1          R.sup.2          a R      b X                                 __________________________________________________________________________      ##STR7##                                                                                        ##STR8##        1 H      1 OC.sub.2 H.sub.5                  C.sub.3 H.sub.7 (i)                                                                             C.sub.3 H.sub.7 (i)                                                                             1 H      1 OC.sub.2 H.sub.5                  C.sub.3 H.sub.7 (i)                                                                             C.sub.3 H.sub.7 (i)                                                                             1 H      2 OCH.sub.2 CH.sub.2 O              C.sub.8 H.sub.17 (i)                                                                            C.sub.8 H.sub.17 (i)                                                                            1 H      1 NH.sub.2                           ##STR9##                         1 CH.sub.3                                                                              1 OC.sub.2 H.sub.5                   ##STR10##                                                                                       ##STR11##       1 H      1 OC.sub.4 H.sub.9 (n)               ##STR12##                                                                                       ##STR13##       1 COOC.sub.2 H.sub.5                                                                    1 OC.sub.2 H.sub.5                   ##STR14##                                                                                       ##STR15##       0 H      1 OC.sub.6 H.sub.13 (n)             H.sub.5 C.sub.2 OC.sub.2 H.sub.4                                                                H.sub.5 C.sub.2 OC.sub.2 H.sub.4                                                                0 H      1 OC.sub.8 H.sub.17 (n)             H.sub.5 C.sub.2 SC.sub.2 H.sub.4                                                                H.sub.5 C.sub. 2 SC.sub.2 H.sub.4                                                               0 H      1                                                                                 ##STR16##                        C.sub.3 H.sub.7 (i)                                                                             C.sub.3 H.sub.7 (i)                                                                             0 H      1                                                                                 ##STR17##                         ##STR18##                                                                                       ##STR19##       0 H      1 OC.sub.2 H.sub.5                  C.sub.8 H.sub.17 (n)                                                                            C.sub.8 H.sub.17 (n)                                                                            0 H      1                                                                                 ##STR20##                         ##STR21##                        0 COOC.sub.2 H.sub.5                                                                    1 OC.sub.2 H.sub.5                  C.sub.4 H.sub.9 (i)                                                                             C.sub.4 H.sub.9 (i)                                                                             0 H      1 OC.sub.2 H.sub.5                   ##STR22##                        0 H      2 OC.sub.2 H.sub.4SC.sub.2                                                       H.sub.4 O                          ##STR23##                        0 H      1 OC.sub.4 H.sub.9 (t)              C.sub.12 H.sub.25 (n)                                                                           C.sub.12 H.sub.25 (n)                                                                           0 H      1 OC.sub.2 H.sub.5                  C.sub.3 H.sub.7 (n)                                                                             C.sub.3 H.sub.7 (n)                                                                             0 H      2                                                                                 ##STR24##                        C.sub.4 H.sub.9 (i)                                                                             C.sub.4 H.sub.9 (i)                                                                             0 H      3                                                                                 ##STR25##                         ##STR26##                                                                                       ##STR27##       0 H      1                                                                                 ##STR28##                        C.sub.5 H.sub.11 (n)                                                                            C.sub.5 H.sub.11 (n)                                                                            0 H      1                                                                                 ##STR29##                        C.sub.6 H.sub.13 (n)                                                                            C.sub.6 H.sub.13 (n)                                                                            0 H      1                                                                                 ##STR30##                        __________________________________________________________________________

A number of compounds of the formula I are known products. They are prepared by methods known per se, for example by the general methods described in "Houben-Weyl, Methoden der organischen Chemie" [Houben-Weyl, Methods of Organic Chemistry], Volume 12, part 2, pages 652-681, (published by Thieme, 1964).

Appropriate alcohols or diols are reacted with PCl₃ to prepare, either directly or via a subsequent reaction between water and the chlorophosphites which have been isolated beforehand, first of all the respective open-chain or cyclic diphosphites of the formula III ##STR31## which are reacted with sulfur/NH₃ in an inert organic solvent to give, via the readily accessible corresponding ammonium monothiophosphates of the formula IV and through subsequent reaction with a suitable halogen compound, the monothiophosphoric acid esters of the formula I. The following reaction diagram illustrates the reaction for the case b=1: ##STR32##

In the formulae I, III and IV, R, R¹, R², X and a are as defined above, Hal is halogen and is preferably chlorine or bromine.

The reaction of 1,3-diols can advantageously also take the form of direct esterification of the diols with H₃ PO₃ (phosphorous acid) to give the corresponding compounds of the formula III.

Other compounds of the formula I are novel and therefore also comprise part of the subject-matter of the invention. They are prepared using methods which are analogous to those given for the known compounds. Novel intermediates of the formulae III and IV therefore also comprise part of the subject-matter of the present invention.

The compounds of the formula I can be used in the crude state, i.e. the state in which they are obtained at the end of their synthesis. They can also be purified before they are used as lubricant additives.

If more than one compound of the formula I are used simultaneously in accordance with the invention, these compounds are admixed to the base oil either singly or mixed.

The compounds of the formula I act as high-pressure additives in lubricants even if present in only very small amounts. For instance, mineral and synthetic lubricating oils, as well as mixtures thereof, to which 0.05 to 5% by weight, based on the lubricant, and preferably 0.1 to 3% by weight of compound of the formula I have been added, have excellent high-pressure lubricating properties. Thus, the lubricant compositions according to the invention are distinguished in particular by a good load-bearing capacity, good wear-prevention properties, and a good friction-reducing action. These ashfree compounds are additionally highly heat-resistant.

The possible lubricants will be familiar to those skilled in the art and are described, for example, in "Schmiermittel Taschenbuch" [Lubricants Handbook] (published by Huthig, Heidelberg, 1974).

The lubricating oil formulation can additionally contain further additives which are added with the intention of improving certain end-use properties. They are preferably antioxidants, metal passivators, rust inhibitors, viscosity index improvers, setting point reducers, dispersants/detergents, thickeners and various known wear-prevention agents, high-pressure agents and friction reducers.

The level of these additives in the lubricant compositions is not restricted. It depends on the chemical structure of the additives and on the field of application and is known to those skilled in the art. Preferably, a number of such additives are combined in order to obtain the most suitable properties.

Examples of antioxidants are:

(a) alkylated and non-alkylated aromatic amines and mixtures thereof, for example dioctyldiphenylamine, mono-t-octylphenyl-α- and -β-naphthylamines, phenothiazine, dioctylphenothiazine, phenyl-α-naphthylamine, N,N'-di-sec.-butyl-p-phenylenediamine;

(b) sterically hindered phenols, for example 2,6-di-tert.-butyl-p-cresol, 4,4'-bis-(2,6-diisopropylphenol), 2,4,6-triisopropylphenol, 2,2'-thio-bis-(4-methyl-6-tert.-butylphenol), 4,4'-methylene-bis-(2,6-di-tert.-butylphenol);

(c) alkyl, aryl or alkaryl phosphites, for example trinonyl phosphite, triphenyl phosphite, diphenyldecyl phosphite;

(d) esters of thiodipropionic acid or thiodiacetic acid, for example dilauryl thiodipropionate or dioctyl thiodiacetate;

(e) salts of carbamic and dithiophosphoric acids, for example antimony diamyldithiocarbamate, zinc diamyldithiophosphate;

(f) combination of two or more antioxidants from among the above additives, for example an alkylated amine and a sterically hindered phenol.

Examples of metal passivators are:

(a) for copper, for example benzotriazole, tetrahydrobenzotriazole, 2-mercaptobenzotriazole, 2,5-dimercaptothiadiazole, salicylidenepropylenediamine, salts of salicylaminoguanidine;

(b) for lead, for example sebacic acid derivatives, quinizarin, propyl gallate;

(c) combination of two or more of the above additives.

Examples of rust inhibitors are:

(a) organic acids, their esters, metal salts and anhydrides, for example N-oleoylsarcosine, sorbitan monooleate, lead naphthenate, dodecylsuccinic anhydride;

(b) nitrogen-containing compounds, for example I. primary, secondary or tertiary aliphatic or cycloaliphatic amines and amine salts of organic and inorganic acids, for example oil-soluble alkylammonium carboxylates; II. heterocyclic compounds, for example substituted imidazolines and oxazolines;

(c) phosphorus-containing compounds, for example amine salts of partial esters of phosphoric acid;

(d) sulfur-containing compounds, for example barium dinonylnaphthalenesulfonates, calcium petroleumsulfonates;

(e) combinations of two or more of the above additives.

Examples of viscosity index improvers are: polymethacrylates, vinylpyrrolidone/methacrylate copolymers, polybutenes, olefin copolymers, styrene/acrylate copolymers.

Examples of setting point reducers are: alkylated naphthalenes, alkylated phenols, polymethacrylates.

Examples of detergents and dispersants are: polyalkenylsuccinimides, oil-soluble metal soaps, such as Ca, Ba, Mg and Al carboxylates, phenylates or sulfonates.

Examples of other wear-prevention additives are: sulfur- and/or phosphorus- and/or halogen-containing compounds, such as sulfurised vegetable oils, zinc dialkyl dithiophosphates, tritolyl phosphate, chlorinated paraffins, alkyl and aryl disulfides.

The subject-matter of the invention also includes the use of compounds of the formula I as lubricant-additives in lubricants, in particular in lubricating oils and greases.

The compounds of the formula I which form part of the subject-matter of the invention are distinguished in particular by good lubricating properties in the mixed friction field at elevated temperatures. They are also highly heat-resistant and ashfree.

The lubricant compositions according to the invention are used in particular in hydraulic oils, gear and engine oils, lubricating greases and metal-machining oils.

The following examples illustrate the invention. Parts and percentages therein are by weight.

EXAMPLE 1

O,O-Dicyclohexyl thiophosphate (ammonium salt)

25.65 parts (0.8 mole) of sulfur are added to a solution of 197 parts (0.8 mole) of dicyclohexyl phosphite in 800 ml of isopropanol, and a moderately fast stream of ammonia is passed in with stirring, during which the temperature is held at about 25° C. by cooling with ice. When all the sulfur has gone into solution, the supply of NH₃ is interrupted, and the mixture is then stirred at room temperature for one hour and at 40° C. for one hour. After addition of 6 parts of active charcoal the mixture is clarified by filtration, and the solvent is distilled in vacuo until the ammonium salt starts to precipitate. The precipitated crystals are filtered off with suction, washed with petroleum ether, and dried in vacuo at 80° C. This produces 191.9 parts (81% of theory) of O,O-dicyclohexyl thiophosphate in the form of colourless crystals having a melting point of 177°-180° C. (as ammonium salt).

    ______________________________________                                         Combustion analysis:                                                                          % N         % P    % S                                          ______________________________________                                         calculated:    4.74        10.49  10.86                                        found:         4.8         10.6   10.7                                         .sup.31 P-NMR analysis (in ppm based on H.sub.3 PO.sub.4): +55.1               ______________________________________                                         ppm.                                                                      

The monothiophosphate ammonium salts given in Table 1 are prepared analogously:

                                      TABLE 1                                      __________________________________________________________________________      ##STR33##                                                                                                     Analysis:                                                    Yield             calculated                                     Example       (% of      .sup.31 PNMR                                                                          found                                          No.  R        theory)                                                                            Melting point                                                                         ppm/H.sub.3 PO.sub.4                                                                  [% P]                                                                              [% S]                                      __________________________________________________________________________     2    n-C.sub.8 H.sub.17                                                                      67% 170-180° C.                                                                    +57.7   8.71                                                                               9.02                                                                       8.7                                                                                9.1                                       3    C.sub.6 H.sub.5                                                                         97% 108-113° C.                                                                    +46.8  10.93                                                                              11.32                                                                      10.5                                                                               11.1                                       4    n-C.sub.4 H.sub.9                                                                       83% 155-160° C.                                                                    +57.7  12.73                                                                              13.18                                                                      12.8                                                                               12.9                                       5    n-C.sub.3 H.sub.7                                                                       91% 151-155° C.                                                                    +58.2  14.39                                                                              14.89                                                                      14.7                                                                               15.1                                       6    i-C.sub.3 H.sub.7                                                                       84% 178-179° C.                                                                    +53.6  14.39                                                                              14.89                                                                      14.5                                                                               15.3                                             ##STR34##                                                                              98% 225-226° C.*                                                                   +55.3  15.55 15.4                                                                         16.1 16.0                                  __________________________________________________________________________      *After recrystallisation from petroleum ether/isopropanol                

EXAMPLE 8

O,O-Diisopropyl-S-(n-hexyl acetate)-thiophosphoric acid

A mixture of 75.36 parts (0.35 mole) of ammonium O,O-diisopropylthiophosphate (Example 6) and 62.55 parts (0.35 mole) of n-hexyl chloroacetate in 600 ml of toluene is heated to 90° C. in the course of one hour and is stirred at this temperature for 12 hours. The precipitated ammonium chloride is then filtered off, and the organic phase of the filtrate is washed with water/sodium hydrogen carbonate and then with water. After drying the solution with anhydrous sodium sulfate the solvent is distilled off in vacuo and the residue is distilled off in an oil pump vacuum at 60° C./6.65×10⁻² mbar, producing 113.75 parts (96% of theory) of O,O-diisopropyl-S-(n-hexyl acetate)-thiophosphoric acid as a colourless liquid. The product thus isolated is further purified by molecular distillation at 60° C./6.65×10⁻³ -1.33×10⁻² mbar. Yield: 91.8 parts (77% of theory) of a colourless liquid having a refractive index (n_(D) ²⁰) of 1.4580. ³¹ P-NMR analysis: 22.8 ppm/H₃ PO₄

    ______________________________________                                         Combustion analysis:                                                                          % C      % H    % P    % S                                      ______________________________________                                         calculated:    49.40    8.59   9.10   9.42                                     found:         49.37    8.43   9.12   9.49                                     ______________________________________                                    

The monothiophosphate esters of the formula I given in Table 2 are prepared analogously, except for Example 10 which is prepared using methods known per se, by addition of O,O-diisopropyl thiophosphate onto ethyl acrylate.

                                      TABLE 2                                      __________________________________________________________________________     Ex-                                               Analysis:                    am-                                         Refractive                                                                           % P                          ple                                                                               Monothiophosphoric acid esters of the formula I                                                                         index calcul.:                                                                            .sup.31 PNMR, in        No.                                                                               R.sup.1   R.sup.2   a R      b X         n.sub.D.sup.20                                                                       found:                                                                              ppm/H.sub.3                                                                    PO.sub.4                __________________________________________________________________________      9 n-C.sub.6 H.sub.13                                                                       n-C.sub.6 H.sub.13                                                                       0 H      1 n-C.sub.6 H.sub.13O                                                                      1.4625                                                                                7.3 +25.7                                                                      7.4                         10.sup.+                                                                          i-C.sub.3 H.sub.7                                                                        i-C.sub.3 H.sub.7                                                                        1 H      1 C.sub.2 H.sub.5 O                                                                        1.4591                                                                               10.4 +24.3                                                                     10.4                         11 i-C.sub.3 H.sub.7                                                                        i-C.sub.3 H.sub.7                                                                        0 H      1 HO        1.4681                                                                               12.1 +23.8                                                                     11.9                         12 i-C.sub.3 H.sub.7                                                                        i-C.sub.3 H.sub.7                                                                        0 H.sub.5 C.sub.2 O.sub.2 C                                                             1 C.sub.2 H.sub.5 O                                                                        1.4542                                                                                8.7 +20.6                                                                      8.3                         13 i-C.sub.8 H.sub.17                                                                       i-C.sub.8 H.sub.17                                                                       0 H      1 H.sub.2 N 1.4801                                                                                7.8 --                                                                         7.8                         14 i-C.sub.8 H.sub.17                                                                       i-C.sub.8 H.sub.17                                                                       0 H      1 C.sub.2 H.sub.5 O                                                                        1.4640                                                                                7.3 +25.7                                                                      7.4                         15 i-C.sub.8 H.sub.17                                                                       i-C.sub.8 H.sub.17                                                                       0 H      1 t-C.sub.4 H.sub.9O                                                                       1.4607                                                                                6.8 +26.0                                                                      7.0                         16 n-C.sub.12 H.sub.25                                                                      n-C.sub.12 H.sub.25                                                                      0 H      1 CH.sub.3 O                                                                               1.4663                                                                                5.9 +25.3                                                                      5.5                         17                                                                                 ##STR35##          0 H      1 n-C.sub.6 H.sub.13O                                                                      1.4823                                                                                9.6 +17.6                   18                                                                                 ##STR36##                                                                                ##STR37##                                                                               0 H      1 i-C.sub.8 H.sub.17 O                                                                     1.5277                                                                                7.1 +18.5                   19                                                                                 ##STR38##                                                                                ##STR39##                                                                               0 H      1                                                                                 ##STR40##                                                                               1.5386                                                                                6.9 +18.7                   20                                                                                 ##STR41##                                                                                ##STR42##                                                                               0 H      1 C.sub.2 H.sub.5 O                                                                        1.5217                                                                                5.1 +18.6                   21                                                                                 ##STR43##                                                                                ##STR44##                                                                               0 H      1 n-C.sub.6 H.sub.13O                                                                      1.4896                                                                                7.4 +23.0                   22 n-C.sub.4 H.sub.9                                                                        n-C.sub.4 H.sub.9                                                                        0 H      4 C(CH.sub.2O).sub.4                                                                       1.4861                                                                               10.3 +25.2                                                                     10.1                         23 i-C.sub.8 H.sub.17                                                                       i-C.sub.8 H.sub.17                                                                       0 H      4 C(CH.sub.2O).sub.4                                                                       1.4808                                                                                7.5 +25.2                                                                      7.5                         24                                                                                 ##STR45##                                                                                ##STR46##                                                                               0 H      1 n-C.sub.6 H.sub.13 O                                                                     1.5373                                                                                7.6 +19.5                   25 i-C.sub.8 H.sub.17                                                                       i-C.sub.8 H.sub.17                                                                       0 H      1                                                                                 ##STR47##                                                                               1.4870                                                                                6.7 +26.1                   26 n-C.sub.3 H.sub.7                                                                        n-C.sub.3 H.sub.7                                                                        0 H      1 n-C.sub.6 H.sub.13                                                                       1.4604                                                                                9.1 +25.3                                                                      9.2                         __________________________________________________________________________

USE EXAMPLES EXAMPLE 30

To test the friction-reducing properties the compounds given below are incorporated into a non-alloyed lubricating oil (viscosity: 139.3 mm². sec⁻¹ /40° C.), and the coefficient of friction is determined at 40° C. and 110° C. by means of an SRV tester (Schwing-Reib-Verschleiss [Vibration-Friction-Wear] tester supplied by the Munich firm of Optimol, see Lubrication Engineering, Vol. 39, No. 11, November 1982, Advertising Index, cover 3, page 729).

In the friction tester used a vibrating sphere (50 Hz) is pressed with a force of 200N against a firmly clamped metal platelet on which there is the oil under test.

Horizontal and vertical forces are measured by means of a piezoelectric pick-up, and the resulting signal is passed through a load amplifier and directly registered on a recorder.

The test results are given in the table below.

                  TABLE 3                                                          ______________________________________                                         (Measurements of coefficient of friction)                                           Additive                  Coefficient of fric-                            Test 4 as per   Test concentration*                                                                           tion μ                                       No.  Example No.                                                                               in %           40° C.                                                                        110° C.                            ______________________________________                                         1    none                      0.148 0.111                                     2    8          1.92           0.077 0.075                                     3    9          2.39                 0.070                                     4    17         1.83           --**  0.072                                     5    24         2.30           0.080 0.066                                     6    26         1.92                 0.054                                     ______________________________________                                          *Test concentration corresponds to a P content of 0.174%, i.e. the             additive concentration was purposely chosen to be such that the                measurements were carried out with the phosphorus concentration the same       for all the additives.                                                         **Not sufficiently soluble at 40° C.                              

The monothiophosphoric acid esters of the formula I which are the subject-matter of the invention, compared with a base oil which contains no additive, have a superior friction-reducing action in the mixed friction field not only at low (40° C.) but also at elevated (110° C.) temperatures. 

We claim:
 1. A lubricant composition which comprises(a) a mineral oil, a synthetic oil or a mixture of said oils, and (b) 0.05 to 5% by weight, based on component (a), of at least one compound of formula I ##STR48## in which a is 0 or 1, b is an integer from 1 to 6, R is --H, --CH₃, --COOH, C₂ -C₁₃ -alkoxycarbonyl where the alkyl radical can be interrupted by one or two oxygen atoms, or is C₆ -C₁₃ -cycloalkoxycarbonyl; R¹ and R², independently of each other, are each C₃ -C₁₂ -alkyl which can be interrupted by one or two oxygen or sulfur atoms, C₅ -C₁₂ -cycloalkyl, phenyl, phenyl substituted by one to three C₁ -C₁₂ -alkyl groups; or C₇ -C₉ -phenylalkyl; or R¹ and R² together can be a bifunctional radical of the formula II ##STR49## where n is 0 or 1, R³, R⁴, R⁵ and R⁶, independently of each other, are each --H, C₁ -C₄ -alkyl, C₅ -C₁₂ -cycloalkyl or phenyl, and R⁷ and R⁸, independently of each other, are each --H, C₁ -C₄ -alkyl, phenyl, --NO₂, C₂ -C₁₉ -alkoxycarbonyl or C₆ -C₁₃ -cycloalkoxycarbonyl, or R⁷ and R⁸, together with the carbon atom to which they are bonded, are a cyclopentenyl or cyclohexenyl ring, andwhen b is 1, X is --OR⁹ or --N(R¹⁰)(R¹¹), where R⁹ is --H, C₁ -C₂₂ -alkyl, C₅ -C₁₂ -cycloalkyl or phenyl, R¹⁰ and R¹¹, independently of each other, are each --H, C₁ -C₂₂ -alkyl, said alkyl interrupted by one or two oxygen atoms, C₂ -C₂₂ -alkenyl or C₅ -C₁₂ -cycloalkyl; or R¹⁰ and R¹¹, together with the nitrogen atom to which they are bonded, are a C₂ -C₂₂ -alkylene or C₂ -C₂₂ -alkenylene ring which can be interrupted by oxygen, sulfur and/or nitrogen atoms, or when b>1, X is a polyvalent radical of the formulae --OC_(m) H_(2m) O--, where the C_(m) H_(2m) group can be interrupted by one or two oxygen or sulfur atoms, --OCH₂ --C(R¹²)(R¹³)--CH₂ O--, ##STR50## (--OCH₂)₃ C--R¹⁴, (--OCH₂)₄ C (--OCH₂)₃ C--CH₂ --O--CH₂ --C(CH₂ O--)₃, where m is an integer from 2 to 40, and R¹² and R¹³ are each C₁ -C₄ -alkyl, C₂ -C₉ -alkoxycarbonyl, C₆ -C₁₃ -cycloalkoxycarbonyl, phenyl or --NO₂, or R¹² and R¹³, together with the carbon atom to which they are bonded, are a cyclopentenyl ring, and R¹⁴ is --CH₃ or --C₂ H₅.
 2. A lubricant composition according to claim 1, where in the compound of formula I, a is O, b is an integer from 1 to 4, R is --H or C₂ -C₅ -alkoxycarbonyl, R¹ and R², independently of each other, are each C₃ -C₁₂ -alkyl which can be interrupted by one or two oxygen atoms, cyclohexyl, phenyl, phenyl substituted by one to three C₁ -C₁₂ -alkyl groups; or benzyl, or R¹ and R² together can be a bifunctional radical of the formula II ##STR51## >here n is 0 or 1, R³, R⁴, R⁵ and R⁶, independently of each other, are each --H, --CH₃ or --C₂ H₅, R⁷ and R⁸, independently of each other, are each --H, C₁ -C₄ -alkyl, phenyl, --NO₂ or C₂ -C₉ -alkoxycarbonyl, or R⁷ and R⁸, together with the carbon atom to which they are bonded, are a cyclohexenyl ring, andwhen b is 1, X is --OR⁹ or --N(R¹⁰)(R¹¹) where R⁹ is --H, C₁ -C₁₃ -alkyl or C₆ -C₉ -cycloalkyl and R¹⁰ and R¹¹ are each --H, or R¹⁰ and R¹¹, together with the nitrogen atom to which they are bonded, are a C₄ -C₆ -alkylene ring which can be interrupted by oxygen, sulfur or nitrogen atoms, or when b>1, X is a polyvalent radical of the formula --OC_(m) H_(2m) O-- where the C_(m) H_(2m) group can be interrupted by one or two oxygen or sulfur atoms and m is a number from 4 to 6, or X is --OCH₂ --C(R¹²)(R¹³)--CH₂ O--, (--OCH₂)₃ C--R¹⁴ or (--OCH₂)₄ C, where R¹² and R¹³ are each C₁ -C₄ -alkyl or C₂ -C₄ -alkoxycarbonyl, or R¹² and R¹³, together with the carbon atom to which they are bonded, are a cyclopentenyl ring, and R¹⁴ is --CH₃ or --C₂ H₅.
 3. A lubricant composition according to claim 2, where in the compound of formula I, R is --H, R¹ and R², independently of each other, are each C₃ -C₁₂ -alkyl, cyclohexyl, phenyl or phenyl substituted by one to three C₁ -C₁₂ -alkyl groups, or R¹ and R² together are a bifunctional radical of the formula II where n is 1, R³, R⁴, R⁵ and R⁶ are each --H and R⁷ and R⁸ are each C₁ -C₄ -alkyl or C₂ -C₃ -alkoxycarbonyl, andwhen b is 1, X is --OR⁹ or --N(R¹⁰)(R¹¹) where R⁹ is --H, C₁ -C₁₃ -alkyl or C₆ -C₉ -cyclohexyl and R¹⁰ and R¹¹ are each --H, or R¹⁰ and R¹¹, together with the nitrogen atom to which they are bonded, are morpholine, thiomorpholino, piperazino or 4-methylpiperazino, or when b>1, X is a polyvalent radical of the formulae --OC_(m) H_(2m) O--, (--OC₂ H₄)₂ O or (--OCH₂)₄ C, where m is an integer from 4 to
 6. 4. A lubricant composition according to claim 1, wherein, in the compound of the formula I, X, when b=1, is --OR⁹ or X, when b>1, is a polyvalent radical of the formulae --OC_(m) H_(2m) O--, --OCH₂ --C(R¹²)(R¹³)--CH₂ O--, ##STR52## (--OCH₂)₃ C--R¹⁴, (--OCH₂)₄ C or (--OCH₂)₃ C--CH₂ --O--CH₂ --(CH₂ O--)₃, where R⁹, R¹², R¹³, R¹⁴ and m are as defined in claim
 1. 5. A lubricant composition according to claim 1, wherein, in the compound of the formula I, b is
 1. 